1. Field of Invention
This invention relates to pharmaceutical tablets. Specifically, this invention provides a nitroglycerin tablet for oral administration which is stabilized to maintain a uniform content of nitroglycerin in the tablets when such tablets are in contact with each other.
2. Description of the Prior Art
Glyceryl trinitrate, hereinafter referred to as nitroglycerin, has been employed in the alleviation of the distress of angina pectoris for many decades. Angina pectoris is a clinical condition which is the result of constrictions developing in the arteries of the heart. When these constrictions develop, angina pectoris patients experience severe pains in the chest from time to time. Nitroglycerin is employed to dilate the cardiac arteries with the subsequent relief of the pain.
Patients afflicted with angina pectoris require an almost immediate response to the drug, not only for the relief of the excruciating pain that is experienced in such attacks, but also for the remission of the fright which often accompanies the pain due to the relationship with the heart. Consequently, nitroglycerin has been formulated in preparations which can be taken orally by the angina pectoris sufferer and provide relief within a very few minutes. Conventionally, nitroglycerin has been formed into what are called molded tablets which contain soluble ingredients and can be placed under the tongue to achieve a rapid onset of the action of the drug.
Nitroglycerin has a vapor pressure of about 0.00026 m.m. at 20.degree. C. Moreover, nitroglycerin is a violent explosive which must be handled with great care. It was found a long time ago that a safe and effective preparation containing nitroglycerin could be prepared by triturating 1 part of nitroglycerin and 9 parts of beta-lactose. This 10 percent nitroglycerin trituration can then be further diluted with other agents for the preparation of tablets of nitroglycerin containing varying amounts of the drug. Not all angina pectoris sufferers require the same amount of nitroglycerin for the relief of the symptoms associated with such a condition. Consequently, it has been conventional in the pharmaceutical art to supply the trade with at least four different strengths of nitroglycerin tablets. These are: 1/400, 1/200, 1/150, and 1/100 grains of nitroglycerin per tablet.
Recently, it has been found that tablets of nitroglycerin, when packaged in a container wherein bulk tablets are in contact with one another, do not maintain a uniform potency with age. However, this lack of uniformity of potency does not indicate a loss of the nitroglycerin per se but rather the migration of the nitroglycerin from one tablet to another when such tablets are in random orientation in contact with each other. It has been found that over a period of a year as much as 20 percent or more of the nitroglycerin in a tablet could be lost by that tablet through contact with another tablet of like composition. Conversely, another tablet could gain as much or more potency through the absorption of migrating nitroglycerin. The exact cause of this phenomenon is not known. However, it is suspected that capillarity may play some part in producing this untoward and totally unacceptable condition.
Accordingly, it is an object of this invention to provide pharmaceutical tablets containing nitroglycerin which are stablized against the migration of the active agent from tablet to tablet when such tablets are in contact with each other in conventional pharmaceutical packaging material.
Another object of this invention is to provide pharmaceutical tablets containing nitroglycerin which are stabilized against the migration of the active agent from tablet to tablet when such tablets are in contact with each other and which can be orally administered for dissolution under a patient's tongue without impairing the rapid solubility of the tablet.
Still another object of the instant invention is to provide pharmaceutical tablets of nitroglycerin which are stabilized against the migration of the active agent from tablet to tablet when such tablets are in contact with each other and which can be administered orally under the tongue with no change in the taste or mouth feel of the tablet.
Another object of the present invention is to provide a method for the preparation of pharmaceutical tablets of nitroglycerin which are stabilized against the migration of the active agent from tablet to tablet when such tablets are in contact with each other.